What is virtual server?

Virtual server is a highly scalable and highly available server
built on a cluster of real servers. The architecture of server cluster
is fully transparent to end users, and the users interact with the
cluster system as if it were only a single high-performance virtual
server. Please consider the following figure.

The real servers and the load balancers may be interconnected by
either high-speed LAN or by geographically dispersed WAN. The load
balancers can dispatch requests to the different servers and make
parallel services of the cluster to appear as a virtual service on a
single IP address, and request dispatching can use IP load balancing
technolgies or application-level load balancing
technologies. Scalability of the system is achieved by transparently
adding or removing nodes in the cluster. High availability is provided
by detecting node or daemon failures and reconfiguring the system
appropriately.

Goals

The basic goal of the Linux Virtual Server Project is to:

Build a high-performance and highly available server
for Linux using clustering technology, which provides good
scalability, reliability and serviceability.

The LVS cluster system is also known as load balancing server cluster.